Process for the improvement of knock rating of gasoline



Nov. 1 8, 1941. M. H. ARvEsoN PROCESS FOR THE IMPROVEMENT OF KNOOKRATING OF GASOLINE Filed June 6, 1938 Patented Novl 418, 1941 PROCESSFOR THE IMPROVEMENT F KNOCK RATING 0F GASOLINE Maurice H. Arveson,Flossmoor, Ill., assignor to Standard Oil Company, Chicago, Ill., acorporation of Indiana Application June 6, 1938, Serial N0. 212,008

14 Claims.

This invention relates to the conversion of hydrocarbons andparticularly to the conversion of low knock rating gasoline intogasolineof high knock rating by treatment with catalysts. Moreparticularly, the process relates to the treatment of straight run,substantially saturated gasolines and naphthas to convert them into agasoline having a high anti-detonating value.l One object of the processis to convert low knock rating motor fuels into high knock rating motorfuels with a minimum loss of motor fuel in the process. Another objectof the process is to effect the conversion of low knock rating motorfuels into high knock rating motor fuels with a minimum heat requirementand at temperatures considerably lower than those heretofore used. Theinvention is illustrated by a drawing which is a now diagram showing thevarious steps of the process.

Heretofore it has been common practice to convert low knock ratinggasolines and naphthasI to high knock rating gasolines by subjectingthem to the reforming process. In that process, the oil, for example,straight run heavy naphtha, is heated to a high temperature, e. g. 950to 1100 F., and cracked sufficientlyl to produce a gasoline usuallyhaving a knock rating of about 72 to 75 octane number from a heavynaphtha having a knock rating of about 35 to 55 octane number. In suchan' operation the gasoline loss usually has amounted to 15 to 25%, theloss consisting mainly of fuel gasesftar and coke. An important objectof my process is to direct the conversion of the knock inducingparaiiinic hydrocarbons into high knock rating gasoline so as to producea minimum of byproduct gases, coke, etc. By myY process the parainichydrocarbons are transformed or isomerized into aromatic hydrocarbons,branched chain olenes and some naphthenic hydrocarbons which have highknock preventing properties when Iemployed in gasoline engine fuel.

Referring to the drawing, a suitable chargingA stock, for examplestraight run heavy naphtha of 10 tov55 octane number from supply tank lI0 is introduced by pump II and line I2 to coil I3 in heater I4. The oilis vaporized and heated to a temperature of 750 to ,900 F. The hotvapors are conducted by line I5 to one of the catalyst chambers I6, twoor more chambers being provided for alternate regeneration hereinafterdescribed. Chambers I6 are charged with a suitable dehydrogenationcatalyst in granular or pelleted form, allowing free passage of thehothydrocarbon vapors therethrough. Various types of catalyst may beemployed for effecting the desired dehydrogenation such as chromiumoxide, chromium oxide gel, metal chromites, etc., such as thosedescribed in patent applications Serial No. 180,301 led December 17,1937, Serial No.

180,302, filed December 17, 1937, now U. S. Patent 2,205,140, and SerialNo. 182,855 filed December 31, 1937, now U. S. Patent 2,205,141. Forexample,

hydroxide, thus producing a chromium oxidegel which, after carefulwashing and drying, may be dehydrated and graded 'to the desired form.

Various modifying agents and promoters may be incorporated in thechromium hydroxide to assist its dehydrogenating action and increase theactive life. Asl an example of such a catalyst, I may use two moischromium hydroxide combined with one mol of zinc hydroxide andy suicientbarium chloride to amount to 5% of the weight of zinc hydroxideemployed.

The hot vapors in traversing catalyst chambers I6 are extensivelydehydrogenated with the production of olefin hydrocarbons and somearomatic hydrocarbons and the products are led by line I1 and line I8 toisomerzation chambers I9. Like chambers I6, chambers I9 are alsoprovided in multiple in order that one or more chambers may be operatingwhile other chambers are being regenerated. Inv chambers v I9 I employ asuitable isomerizing catalyst such as alumina, preferably mounted on.silica gel, Kieselguhr or pumice.

I .may also employ porous forms of carbon, for

example, activated charcoal impregnated with phosphoric acid. Phosphoricacid may also be employed on Kieselguhr. The temperature employed inchambers I9 will usually be lower for example, 60o-'750 F., than thetemperatui'e employed in chambers I6 although with different catalysts,I may employ the same temperature i. e., about 750 to 900 F. or even asomewhat higher temperature i. e., about 900 to 1050 F., bv by-passing aportion of the vapors from line I1, valve line 20, heating coil 2| andthence through line 22 in the order named. 1

In traversing catalyst chambers I9 the unsaturated parain hydrocarbonsare largely rearranged by the catalyst into branched chain and cvclichydrocarbons. Hydrogen present from the dehydrogenation in chambers I6likewise assists in reducing the formation of carbonaceous matter andtar, permitting the isomerizing catalyst in chambers I9 to be operatedat a higher temperature than would otherwise be practicable.

In carrying out the isomerzation of the products of dehydrogenation inchambers I9, itis sometimes desirable to add thereto controlled amountsof water vapor. This may be, done in one of two ways-first, addition ofsteam by line Hato the stream in line I'I wherein it may be passed withthe stream directly to the isomerzation chambers from chambers I6, or belay-passed with hydrocarbon through line 23 to heating coil 2| throughline 22 and line I8 to isomerization chambers I9. The second procedureis to pass the hydrocarbon through lines I1 and I8 directly toisomerization chambers I9 and introduce steam by line 20a into line 20and heating .coil 2l, thence by line 22 to join the hydrocarbon streamin line I8. By thus superheating the steam, theeduction in temperatureof the hydrocarbo in line A -I8 by the addition thereof can be avoidedwhile the temperauue in une ni can be raised without heating thehydrocarbons directly.

The quantities of steam will vary, depending on the type o i' catalyst,the nature 0f the feed stock, but the following general direction can begiven: For every mol' of liquid feed passing through pump I I, .05 to 1mol of water may be added as steam through line I1a.

The vapors leaving chambers I3 are conductedv by line 23 to fractionator24 where they are separatedv into an unvaporized heavy oil fractionwhich is withdrawn by line V25. and a gasoline fraction which iswithdrawn by vapor line 26.

` Heat for fractionation may be supplied by heater 21. Distillate vaporsinline 26 are condensed by condenser 28 and separated in drum 29 whencethe uncondensed gases are withdrawn by line 30 and the liquid productsare removed by line 3| and pump 32 which returns a portion thereof byline 33 to' the upper part of fractionator 24 as a reflux. ATheremaining gasoline the renery, products of higher knock rating',l

e. g., cracked heavy naphtha may -be introduced into the solventextractionstep described, and the rainate thus obtained may be employedas feed stock in tankl III for carrying out the proc- Another method ofseparation which may be used involves azeotropic distillation withvarious polar substances such as liquid S02, acetic acid,`

etc. When a process such as azeotropic distillation is to be used forseparation, itis highly desirable, that the feed through the process bea comparatively narrow cut. It is not necessary that the cutsent'to theprocess be of a xed dis- I tillation range throughout the run or runs,but it is important that at any one instant the feed stock be of narrowboiling range, so that on azeotropic fraction is conducted by line 35 toystabilizing tower 3E heated by heater 31. VThe vapors are withdrawnfrom-the upper part of fractionator 36 vby line 38 and partiallycondensed in condenser 38. Thev condensate and uncondensedgases areseparated in drum 40 and discharged by line 4I while the liquidproducts, consisting mainly of liquid propane with some butane andethane, are withdrawn by line 42 and pump 43. A portion of thecondensate is returned by line '44 tol tower 36 as reflux, the remainingliquid products being discharged by line 45. Gasoline is withdrawn. fromthe base of stabilizer tower 36 by valved line-46 and may be givensuitable chemical treatment such as stabilization against gum formationby the addition of antioxidants, Y

etc.

Depending on the circumstances under which this process is used, it maybe economically desirable to arate the gasoline obtained from line 46into converted and unconverted fractions and recycle the unconvertedfractions with the distillation a satisfactory .separation can be made.y For example, a wide boiling range heavy naphtha may be distilled in abatch-wise operation and the distillate as obtained run immediately tothe process. A naphtha stream of con-` tinually changing boiling rangeis thus obtained but at any given time it has a narrow boiling rangesuitable for separation by azeotropic distillation. The paraflinicfraction so obtained is suitable as charging stock for my process.V

' The gasoline produced in my process willl or- 4 dinarily have a knock'rating of about '10 to 80 octane number, although higher knock ratingsmay be obtained by more extensive dehydrogena- "tion and isomerizationin chambers I6 and I9. This may -be accomplished by reducing the rate ofnow of vapors therethroughand/or increasy ,ing the temperature lof thetreatment. However, if the temperature employed in chambers I6 and I 9is too high cracking will result; and .rapid fouling of the catalystwill `take place, thus requiring 'regeneration at more frequentintervals.

-,When the catalyst in one of the chambers I6" i becomes sumcientlyinactive to prevent its conoriginal feed. The unconverted fractions maybe vent being about 1 to 11/2 volumes per volume of gasoline fed. Theraffinate and extract layers are removed and distilled to removesolvent, the extract being the desired finished product consistingmostly of branched chain oleiins, aromatics and some naphthenes. Theraffinate being predominantly parafllnic, is returned to thedehydrogenation and' isomerization process for y ,further processing.

In the case where highly paramnic, ldw knock tinued use at an economicalrate it may be regenerated by diverting the ow of vapors to a freshcatalyst chamber by means of the valves shown and then sweeping thehydrocarbon vapors from the catalyst chamber with a suitable .inert gas,e. g.,ue gas or steam. For this pur-- pose lines 41 and 48 are employed.After the vapors .are swept from the chamber an oxidizing gas isintroduced into the catalyst chamber for the purpose of burning outcarbonaceous matter deposited on the catalyst. Air maybe used A for thispurpose, preferably diluted with flue gas 1 or other inert., diluent toregulate the rate of Acombustion and avoid excessive temperature rise.

In general the temperature is regulated bythe oxygen concentrationduring the regeneration cycle to avoid heating the catalyst totemperatures\above 1000 F. as it. has been found thathigher'temperatures than this result in a permanent deterioration of thecatalyst. This result may be attained by beginning regeneration with uegas mixed with suilicient air to produce rating feed stocks are notavailable. as such,'in rs an'oxygen concentration ofv about 0.2%, afterwhich the oxygen concentration may be gradually increased as the extentof regeneration progresses. Thermocouples distributed throughout thecatalyst mass serve to indicate the progress of the regeneration.

After regeneration the catalyst may be used 'again and again, theregeneration being repeated until the enlciency falls below aneconomical point. It is not necessary to regenerate the catalyst in thedehydrogenation zone and the isomerization zone, the life of thecatalyst in the two zones being diierent. After repeated regeneration,when the catalyst is deteriorated to a point where it is no longereconomical to'regenerate it further, it may be renewed and the spentcatalyst may be processed to recover valuableingredients. The total lifeof the isomerization and dehydrogenation catalysts are usuallyconsiderably' different, the isomerization catalyst usually having theshorterlife and requiring more frequent renewal. In the case of thephosphoric acid type isomerizing catalyst a portion of the acid may belcst at each regeneration cycle which tends to. reduce the total life ofthe catalyst more rapidly than in the case of the chromium oxidedehydrogenaticn catalysts. y

The pressures employed in my process are 'preferably low. For example, Imay employ atmospheric pressure in both the dehydrogenation and visomerization stages. The pressure in both stages is approximately thesame and infact I may combine the dehydrogenating and isomerizingcatalysts in a single reaction chamber. I prefer to employ moderatepressures in my process,'e. g.,

10 t0 50 pounds per square inch. However, higher pressures may be used,e. g., 200 to 300 pounds per square inch. Although I have describedconducting the dehydrogenating and isomerizing process under conditionswhich produce more extensive decomposition oi the naphtha than simpledehydrogenation, I prefer to regulate the temperature and time oftreating in the catalyst zones to limit the action substantially todehydrogeation thereby producing a treated high knock rating heavynaphtha having approximately the same boiling characteristics as thenaphtha charged to the process thereby avoiding loss of motor fuel byproduction of iixed gases and undesirable light hydrocarbons.-

Although I have described my process in connection with certain speciiicembodiments thereof I intendv that the scope of my invention be limitedonly by the following claims.

I claim:

1. The process o! converting low knock rating parailinic gasoline intohigh.l knock rating aromatic gasoline which comprises subjecting thevapors of said parainic gasoline to the action of a dehydrogenationcatalyst in a first catalyst zone at a temperature of about '150 to 900F. whereby paraiiin hydrocarbons are converted to oleiins and hydrogen,then conducting the combined vapors while still hot through a secondcatalyst zone in contact with an isomerizing catalyst l different fromthe said dehydrogenation catalyst whereby the said olen hydrocarbons arerearranged and thereafter'separating a gasoline motor fuel from theproductsof said reaction.

2. The process oi claim 1 wherein the dehydxiogenation catalyst containsan oxide oi chro- 6. The process' of claim 1 wherein said isomerizationcatalyst is comprised of aluminum oxide. 7. The process of convertingparaillnic naphtha of low knock rating into high knock rating gaso-.line containing substantial amounts of aromatic hydrocarbons, lwhichcomprises vaporizing and heating said naphtha to conversion temperature,conducting a stream of the vapors through a porous bed of adehydrogenating catalyst under dehydrogenating conditions at an elevatedconversion temperature and at a rate sumcient to convert a substantialamount of said paraflinic naphtha to olefine hydrocarbons and hydrogen,conducting the -resulting mixture of hydrocarbons and hydrogen through asecond porous bed of an isomerizing catalyst different fromsaiddehydrogenating catalyst at a high temperature and substantiallywithout condensation of said hydrocarbons whereby said oleflnes aresubstantially converted into aromatic, naphthenic and branched chainolenic hydrocarbons in the presence of said hydrogen and whereby saidhy- 1 drogen reduces the tendency of carbonaceous deposits to form onsaid catalyst, withdrawing the reaction products from said isomerizingcatalyst and separating high knock rating gasoline therefrom byfractional distillation. l

.8. The process of claim 7 wherein the catalytic reactions are conductedat a lpressure of about 3. The process o! claim 1 wherein the saidisomerization catalyst is comprised of phosphoric acid.

A rating` gasoline treated is a straight run heavy naphtha tractionhaving an' octane number between about 10 and 55.

, 4 y 65- 4. The process oi claim 1 whereinthe tem- 10 to 50 lbs. persquare inch.4 9. The process of claim 7 wherein the products of thedehydrogenation reaction are further dehydrogenation catalyst isselected from the class consisting of compounds of chromium andmolybdenum and said isomerizing catalyst is` alumina. v

l2. The process of claim 7 wherein water vapor is added to said mixtureof hydrocarbon vapors' and hydrogen before subjecting to saidisomerizing catalyst.

13. The process of lconverting low knock rating paraiiinic gasoline intohigh knock ratinggasoline which comprises yaporizing said gasoline andsubjecting the vapors thereof, under dehydrogenation conditions, to theaction of a dehydrogenation catalyst in a first catalyst zone.

whereby paraiiinic hydrocarbons are converted to olens and hydrogen,conducting the resulting vapors of hydrocarbons and hydrogensubstantially without condensation through a second catalyst zone, incontact with anisomerization catalyst diierent from said dehydrogenationcatalyst maintaining in said second catalyst zone of isomerization adifferent temperature from the temperature of dehydrogenation maintainedin said nrst catalyst zone, thereby effecting isomerization .of saidolefin hydrocarbons and withdrawing the desired gasoline from saidsecond catalyst zone.

14. 'Ihe process of claim 13 wherein the catalyst employed in saiddehydrogenation zone is a com-'- pound selected from the classconsisting of chromium oxide and molybdenum oxide and the catalystemloyed in said second catalyst zone is alumina.

MAURICE H. ARVESON. j

